Thursday, December 26, 2013

New paper finds Arctic sea ice extent has increased over the last few centuries

A new paper published in Quaternary Science Reviews finds that reconstructed Arctic sea ice extent has increased over the last few centuries. According to the authors, the only sea ice proxy "records having a resolution suitable to document sea ice cover variations over the last centuries" find that "all records show an increase of the sea ice cover over the last centuries" and "a distinct trend for an increased sea ice cover towards modern values over the last centuries."

Excerpt:

"Records having a resolution suitable to document sea ice cover variations over the last centuries have been obtained from the Mackenzie slope, the Beaufort Sea (Richerol et al., 2008; Bringué and Rochon, 2012; Durantou et al., 2012), and the Chukchi Shelf (core B5; de Vernal et al., 2008; Kinnard et al., 2011). At the Beaufort Sea sites, the variations are of limited amplitude and the estimates are close to “modern” observations, but all records show an increase of the sea ice cover over the last centuries. At the Chukchi site, the record shows large amplitude variations with a distinct trend for an increased sea ice cover towards modern values over the last centuries."

Sea ice cover extent expressed in terms of mean annual concentration was reconstructed from theapplication of the modern analogue technique to dinocyst assemblages. The use of an updated database, which includes 1492 sites and 66 taxa, yields sea ice concentration estimates with an accuracy of 1.1/10. Holocene reconstructions of sea ice cover were made from dinocyst counts in 35 cores of the northern North Atlantic and Arctic seas. In the Canadian Arctic, the results show high sea ice concentration (>7/10) with little variations throughout the interval. In contrast, in Arctic areas such as the Chukchi Sea and the Barents Sea, the reconstructions show large amplitude variations of sea ice cover suggesting millennial type oscillations with a pacing almost opposite in western vs. eastern Arctic. Other records show tenuous changes with some regionalism either in trends or sea ice cover variability. During the mid-Holocene, and notably at 6 0.5 ka, minimum sea ice concentration is recorded in the eastern Fram Strait, northern Bafﬁn Bay and Labrador Sea. However, this minimum cannot be extrapolated at the scale of the Arctic and circum-Arctic. The comparison of recent observations and reconstructions suggests larger variations in the Arctic sea ice cover during the last decades than throughout the Holocene.